The proposed research project is designed to study certain aspects of exocytosis and endocytosis of lysosomal enzymes in man and to elucidate the basis defect in the fetal neurodegenerative disorder known as I-cell disease (mucolipidosis II). A prominent characteristic of the disease in vitro is a preferential exocytosis of lysosomal enzymes from cultured fibroblasts. The initial approach will be to study the abnormal exocytosis of these enzymes; specifically, beta-hexosaminidase, from I-cell fibroblasts and from normal fibroblasts in which the I-cell phenomenon has been stimulated by treatment with agents such as chloroquine, colchicine or Cytochalasin B; all known to have specific effects on secretory processes in cells by acting on membrane stability or on microtubules and microfilaments. A study of the characteristics of lysosomal enzymes excreted by osteoclasts during bone resorption, by phagocytic cells, and by prostatic secretory cells will be undertaken to assess whether physiological exocytosis mechanisms may account for the presence and characteristics of lysosomal enzymes in normal human plasma and seminal fluid. The hypothesis that, in mesenchymal tissues, lysosomal enzymes are normally excreted, then endocytosed for final processing by neighboring cells through specific carbohydrate-mediated recognition sites on the enzymes, will be explored in assessing the extent to which these mechanisms may be altered in fibroblasts from patients with I-cell disease. Finally, identification of the terminal carbohydrate residues in the recognition sites on normal beta-hexosaminidase will be undertaken to determine which residue(s) are involved in specific enzyme uptake by cell receptors.